This invention relates to an improved deposition apparatus and process for depositing a material on a substrate.
A layer of a material, such as a tungsten layer, can be deposited on a substrate, such as a semiconductor wafer or a flat panel display, using a chemical vapor deposition (CVD) process or physical deposition process. Exemplary of such processes is the deposition of tungsten on a semiconductor wafer using a CVD process. In this process, the substrate is loaded into a deposition chamber from a load lock chamber, and conventionally mounted horizontally in the deposition chamber with an upper deposition surface of the substrate facing toward incoming process gases. The deposition gases are usually emitted to the deposition chamber containing the wafer from a gas inlet or "shower head" located near the top of the CVD chamber. The chamber has a process gas section in contact with the deposition surface of the wafer, and a gas purge section. The process gas section and the gas purge section are separated by a horizontally extending barrier, which is conventionally known as a pumping plate.
After deposition of metal on the wafer, the wafer is removed from the deposition chamber through a slit valve into the load lock chamber. At that time, purge gases are introduced into the gas purge section of the chamber from the load lock chamber when the slit valve is open. The purge gas removes residual process gases and contaminants such as reaction byproducts from the chamber. It is important to do this so that the deposition chamber and other chambers of the metal deposition system, such as a wafer loading chamber and a wafer removal chamber, remain clean. Residual process gases can result in formation of particulate contaminants. Contamination of these chambers by particles can result in particle deposition on the product, which in most cases renders the product unusable. The purge gas from the load lock chamber, typically nitrogen, flows through the gas purge section, through an opening between a shadow ring and the wafer, into the process gas input section, and from there into a vacuum manifold system.
A problem that has been encountered is that the purge gas moves the wafer. This can lead to unloading errors resulting in damage to the wafer, and interruption of the automatic production process. These unloading errors occur because the wafer is not found at its designated position by the pickup mechanism due to the movement caused by the purge gas. Lost production due to damaged wafers and the downtime resulting from this problem lowers production rates, thereby increasing production costs.
Accordingly, there is a need for an apparatus and a method for depositing a material on a substrate, where spent process gas and byproducts of the process gas can be purged from the deposition chamber, without unloading errors caused by movement of the substrate during the purge.